Nebulizer heater

ABSTRACT

A nebulizer providing a moistened breathing mixture of aerosol for inhalation therapy is provided with an improved accumulator chamber and heater configured to heat aerosol discharged from the nebulizer so as to most efficiently utilize the heat energy and to most efficiently transfer heat energy from the heater to the aerosol. Passage of the aerosol through and accumulation in a relatively long annular accumulator chamber that adjoins the heater allows introduction of heated water vapor into the aerosol. A central chamber collects precipitated droplets from the mixing chamber, and a wicking disc flows the collected liquid, under pressure or by wicking action, into the accumulator chamber where it is heated and vaporized.

This application is a continuation-in-part application of applicationSer. No. 422,310, filed Oct. 16, 1989 for Nebulizer Heater now U.S. Pat.No. 5,063,921, which in turn is a continuation-in-part of applicationSer. No. 280,550, filed Dec. 6, 1988, for Nebulizer Heater (nowabandoned), which in turn is a continuation-in-part application ofapplication Ser. No. 120,080, filed Nov. 12, 1987 for Nebulizer Heater,now U.S. Pat. No. 4,819,625.

BACKGROUND OF THE INVENTION

The present invention relates to nebulizers for inhalation therapy, andmore particularly concerns a nebulizer having improved arrangements forheating both the container liquid and the aerosol produced by thenebulizer, and for collecting and vaporizing precipitated liquiddroplets.

Nebulizers are commonly used for inhalation therapy to provide moistwarm oxygen enriched breathing mixture to the patient. In many types ofnebulizers a stream of oxygen is passed through a restrictive nozzle toincrease its velocity and provide a venturi effect that sucks liquidfrom a container connected with a mixing chamber. The high speed streamof oxygen is mixed with ambient pressurized air and entrains water thatis drawn up from the container by the low pressure of the venturi effectof the oxygen stream of high velocity.

The aerosol breathing mixture reaching the patient must have atemperature not less than ambient room temperature and moreover shouldhave a significant content of water vapor. Various factors tend to lowerthe aerosol temperature including the relatively long path of aerosolflow through the tubing from the nebulizer to the patient and, inparticular, the operation of the air water and oxygen mixing chamber,which often involves a decreased pressure due to at least the venturiaction of the high speed jet. In the mixing chamber, expansion of thecompressed oxygen will lower its pressure and thus effectively decreasethe temperature of the resulting aerosol.

Many attempts have been made to heat either the aerosol or the containerliquid but these have not been successful. Nebulizer heaters presentlyavailable are considered to be unsatisfactory. It is difficult to heatthe aerosol directly, because the mixture, which is basically a gas, haslow heat transmissivity, and thus efficiency of prior aerosol heatershas been low. Attempts to heat the aerosol by heating the water in thecontainer before it is mixed with the air oxygen mixture also have beenunsatisfactory in that it is difficult to transfer sufficient amounts ofheat to the aerosol by means of heating the water. Moreover, havingraised the temperature of the resulting aerosol by heating the water,the aerosol becomes more susceptible to "rain out", which means thatwater vapor in the aerosol tends to condense into larger droplets and tofall from the aerosol into the connecting tubing. The problem of watercollecting in the connecting tubing between the nebulizer and thepatient is significant, not only because of the fact that the aerosolreaching the patient has less moisture, but because water collecting inthe tubing could block the tubing and prevent flow of any inhalationmixture to the patient. No nebulizers are known that increase entrainedwater content of the aerosol by introducing water vapor produced by aheater.

Accordingly it is an object of the present invention to provide anaerosol heater that avoids or minimizes above mentioned problems.

SUMMARY OF THE INVENTION

In carrying out principles of the present invention in accordance withone embodiment thereof, an accumulator housing connected to a heaterhousing cooperates with a heated platen to define an aerosol accumulatorchamber with a precipitate flow tube extending from the aerosol mixingchamber of the nebulizer mixing body and through the accumulatorchamber, to define a peripheral accumulator passage within theaccumulator housing, and to define a gap for controlled flow ofprecipitate from the lower end of the precipitate flow tube to theaccumulator passage. Collected precipitate is heated and vaporized inthe accumulator passage and returned to the aerosol. The precipitateflow tube is pressurized to aid flow of precipitate to the accumulatorpassage. One embodiment of the invention maximizes collection ofprecipitated droplets for flow to the heated accumulator passage insteadof return to the liquid container. Aerosol from the aerosol mixingchamber is conducted by a conduit into the peripheral accumulatorpassage and exits therefrom to provide a heated aerosol stream forinhalation therapy. Introduction into the aerosol of water vaporgenerated by the heated platen in the bottom of the aerosol chamberenhances both increased moisture content and increased temperature ofthe aerosol. In one embodiment means are provided to induce controlledflow of collected water to the heater platen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial view of a nebulizer and heater embodyingprinciples of the present invention;

FIG. 2 is a section taken on lines 2--2 of FIG. 1;

FIG. 3 is a section taken on lines 3--3 of FIG. 2;

FIG. 4 is a fragmentary sectional view showing details of the coatedplastic that forms structural elements of the heater housing;

FIG. 5 is a perspective illustration of a modified form of the nebulizerand modified heater;

FIG. 6 is a vertical section taken on lines 6--6 of FIG. 5;

FIG. 7 is a horizontal section taken on lines 7--7 of FIG. 6;

FIG. 8 is an enlarged fragmentary view showing the relation between anend of the precipitate flow tube and the heater plate of the embodimentof FIG. 5;

FIG. 9 is an exploded perspective view showing major components of theembodiment illustrated in FIG. 5;

FIG. 10 is a vertical section of another embodiment of nebulizer andheater;

FIG. 11 is a pictorial illustration of a venturi tube and dropletcollection plate of the embodiment of FIG. 10;

FIG. 12 is a pictorial illustration of a flow inducing control disc thatmay be used with any of the nebulizers described herein; and

FIG. 13 is a vertical section of a portion of the embodiment of FIGS. 10and 11 showing the flow inducing control disc of FIG. 12 on the heaterplaten.

DETAILED DESCRIPTION

As illustrated in FIG. 1 a nebulizer, generally indicated at 10,includes a container 12 having its lower portion resting upon andgenerally confined in a base type heater, generally indicated at 14. Thenebulizer may be of the type shown in U.S. Pat. No. 4,629,590 toBagwell, which describes a nebulizer sold by CIMCO, assignee of thepresent application. U.S. Pat. No. 4,629,590 is owned by such assignee.The nebulizer container 12 confines a body of sterile water and includesan upper portion having secured thereto a mixer 16, which receivesoxygen under pressure from an oxygen input conduit 18. By means of amixing jet (not shown in FIG. 1) contained within the mixer 16, liquidis drawn from the bottom of the container 12 for mixing in an aerosolmixing chamber with the pressurized oxygen and with ambient air drawninto the mixing chamber through an aperture 20 in the mixer. Thus, themixer of the nebulizer provides a output stream, via an output fitting22, of an aerosol, which is a moisturized mixture of air and oxygen foruse in inhalation therapy. Further details of this nebulizer are shownin U.S. Pat. No. 4,629,590. FIGS. 5-9, described below, also showfurther details of the gas/water mixing jet. The construction details ofthe gas/water mixing arrangement of the embodiment of FIGS. 5-9 may beused in the embodiment of FIGS. 1-4.

According to the present invention a heater assembly 14 is provided toperform a number of different functions. First, the heater assemblyprovides a support and a base upon which the nebulizer rests. Second,the heater assembly provides direct heat transfer to the bottom andsides of the bottom of the container 12, to directly heat water withinthe container. Third, the heater assembly provides an elongated aerosolaccumulator of high volume and large cross sectional area for heatingthe aerosol provided by the nebulizer. This aerosol accumulator receivesaerosol produced by the nebulizer via a connecting conduit 24, havingone end connected to the nebulizer output fitting 22 and the other endconnected to an input fitting 26 on the heater assembly. The aerosolaccumulator within the heater assembly terminates in an output fitting28, to which is connected an output conduit 30 that is connected to apatient breathing apparatus (not shown).

A fourth function of the described heater assembly is its collection ofrain out from the aerosol of the nebulizer as it flows through and istemporarily stored in the aerosol passage. The heater assembly heatsprecipitated water droplets to re-vaporize the water so that it will beagain entrained within the nebulizer aerosol.

The heater assembly comprises a heat transfer housing, illustrated incross section in FIG. 2, having a circular top support plate 34 and adepending continuous peripheral wall 36 fixed to the outer edges of theplate 34. A second continuous peripheral wall 38, spaced from the innerwall 36 and running parallel thereto, completely encircles the innerwall 36 and is fixedly connected to the bottom of the inner wall 36 by acontinuous annular bottom wall 40, fixedly secured to the bottoms ofboth the inner and outer walls 36 and 38. Walls 36, 38 and 40 preferablyare integral with top plate 34. Fixedly connected to and extendingacross upper edges 42, 44 of inner and outer walls 36 and 38 is acontinuous annular top wall 50, which cooperates with the sidewalls 36,38 and bottom wall 40 to provide a sealed completely closed continuousannular aerosol passage and accumulator 52.

As best seen in FIG. 3 tubular input and output fittings 26, 28 areintegrally formed with the circular outer wall 38 and a single baffle orpartition 54 extends across the aerosol passage, from the inner wall 36to the outer wall 38, so as to provide a continuous flow aerosolaccumulator passage and temporary storage chamber. Aerosol will flow inthrough fitting 26, thence in a clockwise direction, as indicated by thearrows, around the aerosol accumulator passage 52, and thence outwardlythrough output fitting 28. Aerosol remains in the accumulator 52 becauseof its relatively large volume and because its cross sectional area ismade larger than that of the input and output ports and conduits.

A relatively short rigid upstanding container support wall 5 is fixed tothe outer edge of top plate 34 and to the upper edge of inner wall 36and extends continuously around the bottom of container 12 to confinethe bottom of the container within a heater recess formed by supportwall 58 and top plate 34. Top plate 34 and inner wall 36 cooperativelydefine a downwardly facing heater mounting chamber of generally circularcylindrical form which snugly mounts a circular cylindrical and heatconductive heater housing 60 containing suitable heater elements (notshown). Heater housing 60 may be secured within the heater chamber andto the top plate 34 by means of fastener means such as for example ascrew 62. Heater housing 60 includes a heater housing bottom plate 64 ofcircular configuration and extending along and in heat conductivecontact with the full extent of bottom wall 40, to provide maximum heatflow from the heater to the bottom plate.

The heat transfer housing and the heater housing 60 are mounted in aheater assembly housing formed of an inter-fitting base 68 and a heaterassembly housing top 70. Housing base 68, formed of a suitable rigidplastic, is of a circular configuration, having four mutually spaced andfixed internal supporting posts 74, 76, and others (not shown)projecting upwardly from a bottom 80 of the base 68. Each post has avertically extending threaded aperture for receiving respective ones ofa plurality of screws 82, 84, 86 and 88, (FIG. 3) which extend throughthe heater housing bottom plate 64 into the apertures in supportingposts 74, 76 etc. The assembly housing top part 70 has a centralaperture 90, through which the bottom of the container 1 extends forsupport by the heater top support plate 34. Inner edges of the aperturedtop of assembly housing top 70 rest on upper edges of container supportwall 58. A peripheral flange 94, outwardly extending from the assemblyhousing top, cooperates with a pair of oppositely positioned pivotedlatches 96 (only one of which is shown) mounted on the assembly housingbase 68 to detachably secure the two parts of the assembly housing toone another. A manually operable switch 100, (FIG. 1) mounted on theassembly housing base 68 is provided to control the heater elementswhich are connected to a suitable source of electrical power by means ofan electrical lead and temperature regulating circuitry or the like (notshown), that may be mounted within assembly housing base 68 below theheater housing bottom plate 64. The top and bottom parts of the assemblyhousing are provided with mating semicircular recesses to form circularapertures (FIG. 3) 104, 106 through which the fittings 26 and 28 extend.

The entire heater assembly is supported on four legs, of which three,indicated at 110, 112, and 114 are shown, which are formed integrallywith and depend from the bottom 80 of the bottom part of the heaterassembly base 68.

Heater housing 60 and its bottom plate 64 are made of a suitable metalhaving high heat conductivity such as for example aluminum, whereas theheat transfer housing is made of a light weight plastic having improvedheat transfer and cleaning characteristics provided by a heavy metalcoating. Thus, as illustrated in FIG. 4, the heat transfer housingincluding top support plate 34, walls 36, 38, and 40, (but not walls 50and 58) are formed of a plastic material 120 coated on both sides withheavy, thick coatings 122, 124 of suitable metal. Presently preferredfor such coatings are combinations of electroless copper, electrolessnickel and chromium, formed in layers, one upon the other and depositedupon both sides of the interposed plastic 120. By this means the plasticis provided with good heat transfer characteristics and a smooth easilycleaned surface, and the parts are still readily manufactured ofinexpensive and readily formed plastic. The entire heat transfer housingis readily removable for sterilization. Walls 50, 58 are made of thesame plastic as the other walls, but need not be coated with metal.

In operation of the device, oxygen under pressure is fed to the mixer 16via oxygen input conduit 18 and mixed with fine water droplets or vaporderived from water contained in the container 12 to provide an aerosoldischarge via fitting 22 and connecting the conduit 24. The aerosolflows from the conduit 24 through heater assembly input fitting 26 andthence in a substantially 360 degree path through the aerosolaccumulator and passage 52 which closely encircles the heater chamberthat contains the heater housing 60. Aerosol remains in the accumulatorfor a relatively increased time. Aerosol then flows through the outputport 28 to connecting tubing 30. The container 12, which is resting uponheat transfer housing plate 34 and confined within the circularcontainer support wall 58, has its contents heated by transfer of heatfrom the heater through the plate 34. Temperature of the aerosol israised by using water heated in the container by the heater and also bytemporarily retaining the aerosol in the accumulator adjacent the verysame heater that heats the container. Flow of aerosol through thepassage or accumulator 52 is of long duration. Thus, time of storage inaccumulator 52 is sufficient to heat the aerosol. Moreover, liquidcollecting in the bottom of the passage, due to rain out from theaerosol, is heated, vaporized and recombined with the flowing aerosol.Thus the described heater is effective not only to heat the aerosolprovided from the apparatus but also significantly improves its moisturecontent.

The entire apparatus is readily disassembled for cleaning andsterilization. To disassemble the apparatus, latches 96 are disengagedand the hoses are disconnected. Container 12 is removed from the heaterassembly and the assembly housing top 70 is removed from the base 68.The heat transfer housing, comprising the walls 36, 38, top supportplate 34, bottom plate 40, and walls 50 and 58 are readily removed as anintegral unit from the heater housing 60 which remains fixably securedto the assembly housing base 68 by means of the screws 82 through 88.The heat transfer housing may then be readily cleaned and sterilized.The chromium plated surfaces of the aerosol passage and of the heattransfer housing top plate 34 are smooth and readily cleaned andsterilized.

The described heater assembly is easily adapted for use with nebulizersof different types and different configurations. It is only necessary tochange the configuration of the container receiving recess defined bythe top support plate 34 and support wall 58, and also the size ofopening 90, to enable the heater to receive, support and operate upon anebulizer having a container of different size, shape or configuration.

The assembly housing provides protection for the heating unit and theheat transfer housing. It prevents heat loss and also protects thecontrols and electric elements from accidental spillage of water. Thehousing serves as an insulator and also prevents accidental contact withelectrical elements within the assembly housing base.

As mentioned above, a significant aspect of the described constructionand configuration of the heater is the fact that the aerosol accumulatoror passage not only has a relatively large volume but also has a largecross sectional area. In a presently preferred embodiment the crosssectional area of the annular aerosol passage 52 is approximately twicethe cross sectional area of either of the conduits 24 or 30, which areof a size normally employed in devices of this kind. The increasedvolume and area of the aerosol passage provides a number of advantages.The large volume causes the annular passage to act as an accumulator orreservoir so that aerosol produced by and discharged from the mixer 16is effectively stored in the passage 52 for a period of time before itis discharged through the relatively small cross sectional area outputport 28. Thus, because the formed aerosol is stored for a short periodof time within the accumulator or chamber 52, there is more time forlarge water droplets to be precipitated from the aerosol and,importantly, there is more time for the accumulated water alreadyprecipitated in the accumulator chamber to be vaporized andre-introduced into the aerosol within the accumulator chamber. Anotheradvantage of the relatively large cross sectional area of theaccumulator 52 is the fact that it has a larger surface area to providea much greater area of contact between its heated wall and the aerosolthat is temporarily stored therein.

In the embodiment illustrated in FIGS. 1 through 4, the nebulizer andcontainer are made and sold as an integral sealed unit complete with acontainer carrying its body of sterile water. Some nebulizers are madewith the mixing head separate from the container and are arranged to beconnected at the time of use to a separately manufactured, handled andstored sterile water container. In such an arrangement the nebulizermixing head is generally provided with a lower portion having a femalethread that is adapted to mate with a male thread on the top of aseparate container of sterile water, with the nebulizer suction tubewithdrawing water from the container into the mixing chamber under thenebulizer venturi action, the suction tube being extended from thenebulizer head down into the container when assembled.

Principles of the present invention may be arranged for use with such acombined assembly of separate nebulizer mixing head and separate sterilewater container in a manner illustrated in FIGS. 5 through 9. As shownin FIG. 5, a separate nebulizer head and mixing means is identifiedgenerally by numeral 120 and is combined with a separate and independentsterile water container, indicated by reference numeral 122 (only theupper portion of which is shown in FIG. 5). These major components areillustrated in the exploded (disconnected) view of FIG. 9. Commonly,nebulizer head 120 is connected directly to the container 122. However,according to principles of the present invention, as incorporated in theembodiment of FIGS. 5 through 9, an aerosol accumulator housing 124 anda heater assembly 126 are interposed between the mixing head 120 andcontainer 122 with all four units threadedly interconnected to oneanother in an end to end relation, as can be seen in FIGS. 5 and 6. Thenebulizer mixer head comprises a mixer body or housing 130 (FIG. 6),having an input fitting 132 to which may be connected a hose 134 whichitself is connected to a source of oxygen under pressure (not shown).Mixer body 130 includes a nozzle fitting 136, having a high velocity jetorifice for introducing pressurized oxygen from tube 134 to the interior138 of the mixer body. A suction tube 140 is connected to nozzle fitting136 and has an outlet orifice adjacent the jet orifice. Suction tube 140extends downwardly through all of the components and has a lower suctionend thereof submerged in a body of liquid (generally sterile water) 142confined in container 122. One or more ports 137 are formed in mixerbody 130 for introducing ambient air to the interior of the mixer bodyto be mixed with the oxygen and water.

Mixer body 130 includes a downwardly tapered aerosol mixing chamberhousing section 144, in communication with the interior 138 of the body130, and an output fitting 146 for discharging mixed aerosol from theaerosol mixing chamber 144. The lower end of chamber 144 is formed withan internally threaded connecting nipple 148, and at its lower end has arelatively large diameter passage 150 for allowing water dropletsprecipitated from aerosol within the mixing chamber 144 to flow or falldownwardly from the chamber.

An accumulator 124 includes a housing 152 of generally right circularcylindrical configuration, having a fixed top plate 154 formed with anupwardly extending externally threaded connecting fitting 156, having abore 158, and adapted to threadedly engage the lower threaded fitting148 of the aerosol mixing chamber.

Accumulator housing 152 has an open bottom end formed with externalthreads 160 and includes an external circumferential serrated ring 162just above its threaded end to facilitate turning of the accumulatorhousing. A sealing o-ring 164 extends around the connecting fitting ofthe accumulator housing at the upper end of threads 160.

Fixed to the top plate 154 of the accumulator housing, in substantialalignment and coextensive with the interior bore 158 of connectingfitting 156, is a precipitate flow tube 170, of circular cross section,extending downwardly for substantially the full height of theaccumulator housing. The precipitate flow tube 170 cooperates with theexterior wall of the accumulator housing to effectively define anannular aerosol accumulator passage 172 within the interior of theaccumulator housing and surrounding the tube 170. Input and outputfittings 173 and 174, respectively, are connected to input and outputports formed in the accumulator housing and positioned as best shown inFIGS. 5 and 7. Input and output fittings 173 and 174 are illustrated indotted lines in FIG. 6 as being on opposite sides of the accumulatorhousing but are shown in such positions solely for clarity ofillustration and to enable the showing of both such fittings in thevertical section of FIG. 6. The correct position of fittings 173,174 isas shown in FIGS. 5 and 7. A connecting conduit 176 (FIG. 5)interconnects output fitting 146 of the nebulizer head with the inputfitting 173 of the accumulator housing. The actual position of thisconnecting conduit is outside of the nebulizer head 120 and outside ofaccumulator housing 124, as shown in FIGS. 5 and 7, but the conduit isshown in dotted lines in FIG. 6 to provide a full, but somewhatschematic, showing in this figure of the interconnection of theaccumulator and mixer head.

Heater 126 is formed with a substantially right circular cylindricalhousing 180, defining a heater chamber 182 in which is mounted anannular shaped heater 184 (FIG. 8). Heater 184 is in contact with aheater platen 186 (see FIGS. 6 and 8) which extends across and seals theupper end of the heater chamber 182. The heater plate is a thin metallicplate, sealing the heater chamber but having a central opening in whichis seated an apertured grommet or sealing plug 188. Suction tube 140extends from the fitting 136 downwardly through the aerosol mixingchamber 138, through the precipitate flow tube 170, completely throughthe aperture of the sealing plug 188, through the center of the heaterchamber 182, and into the liquid 142 contained in container 122. Theplug 188 collects and sheds water droplets that collect on the suctiontube and prevents such water from flowing back into the container. Theplug sheds such collected water to the heater platen to flow beneath thelower end of tube 170 into the accumulator chamber.

Heater housing 180 has an upper end portion 189 internally threaded toreceive the external threads 160 of the lower connecting end of theaccumulator housing, so that when the accumulator housing and heaterhousing are connected as shown in FIG. 6, sealing o-ring 164 iscompressed between the upper end of the heater housing and the serratedring 162, to seal the two together. A centrally located cylindricalmember 190 extends vertically through the heater housing, receiving thelower end of sealing plug 188 and providing a central guideway for thesuction tube 140.

The lower end of heater housing 180 is formed with a threaded connectingfitting, having two concentric internal connecting threads of mutuallydifferent diameters. Thus, a large diameter connecting thread 192 isprovided for threaded connection with a container (not shown), having arelatively large diameter male connector at its upper end. The lower endof the heater housing also has a smaller diameter internally threadedconnector 194 that threadedly connects to the externally threaded neck196 of container 122. Although the assembly is shown as composed of fourbasic units, mixer head 120, accumulator chamber 124, heater 126, andcontainer 122, all threadedly interconnected to one another in end toend relation, it will be readily appreciated that any two or more of thefour components parts may be made with fixed interconnection betweenthem. For example, the mixer head, accumulator housing and heater allmay be fixedly and permanently connected to one another. In such anarrangement this assembly of the three upper components is capable ofbeing detachably and threadedly connected to an independent, separatesealed sterile container, such as container 122. Alternatively, theaccumulator housing and heater may be permanently connected to oneanother, and appropriate threaded fittings provided on the upper end ofthe accumulator housing and the lower end of the heater for connectionto different types of aerosol mixing heads and sterile containers.

An important feature of the present invention is the position andrelative location of the lower end of precipitate flow tube 170. This isbest shown in FIGS. 6 and 8. The lower end 200 of tube 170 is positionedclosely adjacent to but spaced from the heater platen 186 to provide aflow gap 202 that is approximately 0.03 inch in height. Water droplets,liquid precipitate, falling from the aerosol in aerosol mixing chamber138,144, drop through the bore 158 of the lower end fitting 148 of theaerosol mixing chamber, and then through the precipitate flow tube 170to fall upon the upper surface of heater platen 186, which is heateddirectly by the heater element 184. Droplets also collect on theinterior of chamber walls 144 and upon the exterior of the suction tube140 (in the mixing chamber) and flow downwardly along the surfaces to becollected at the lower end of tube 170. The heater is such as to providea temperature of the platen of as high as 130° C. Temperature of theheater platen is adjustable by means of a temperature control knob 206,FIG. 5, and power to the heater is controlled by on/off switch 208. Withheater platen temperatures at or near boiling, water droplets fallingthrough the flow tube 170 to the heater platen are quickly heated andare drawn from or caused to flow outwardly from the area of the heaterplaten directly underneath the flow tube 170 radially outwardly into theperipheral aerosol accumulator chamber 172. These water droplets arecaused to flow radially outwardly through a capillary passage formed bythe gap 202 by a combination of forces, including a capillary actionthat results from the very small size of the gap 202 and the increasedpressure in the interior of mixing chamber 144. This increased pressureis caused in part by the pressurized oxygen input from oxygen input tube134. The accumulator chamber is connected via its output port 174, andtherefore is at substantially ambient pressure, to provide adifferential pressure between mixing chamber 144 and the accumulatorchamber that helps drive water through the gap. The very small gapensures that precipitated water droplets not only contact the heaterplaten 186, but are caused to flow along its surface, and thus remain incontact with the heater platen for an increased period of time, therebyincreasing the efficiency of the water vaporization that is accomplishedby the heater plate. The heater platen vaporizes water dropletsprecipitated from the aerosol mixture in the mixing chamber 144 and alsothose droplets precipitated from the aerosol flowing through theaccumulator passage 172. Heated water vapor is thus generated by theheated platen at the bottom of the accumulator passage 172 and is mixedwith aerosol in the passage. This accomplishes two desired results. Theheated vapor efficiently increases aerosol temperature and efficientlyincreases moisture content of the aerosol.

In operation of the nebulizer and heater of FIGS. 5-9, oxygen flowingunder pressure from input tube 134 is projected at high velocity fromthe orifice of jet nozzle fitting 136, providing a slightly lowerpressure that accompanies the high speed oxygen stream adjacent theupper end of the suction tube 140. Enough suction is created by the highvelocity stream to draw liquid from the container 122, through thesuction tube into the mixing chamber 138. Ambient air is also drawn inthrough ports 137 to provide an aerosol mixture of water, oxygen and airthat flows downwardly into the aerosol mixing chamber 144. The aerosolswirls about and is mixed in this chamber, then flows through thedischarge port 146, through connecting conduit 176, and into the aerosolaccumulator passage via input fitting 173. The aerosol flows around thepassage 172, in the directions indicted by the arrows in FIG. 7, andafter one or more revolutions will flow outwardly through output fitting174, where it is fed via an output tube 210 to a patient's breathingapparatus. The aerosol dwells for a relatively long time in the longperipheral passage 172 of the accumulator, and thus is effectivelyheated by the platen 186.

During passage of the aerosol through the accumulator chamber, waterdroplets that have fallen through or flowed along walls of precipitateflow tube 170 and have flowed along the outside of the suction tubecollect at the bottom of the precipitate flow tube. The collecteddroplets are driven through narrow gap 202 to be vaporized by the heaterplaten 186 and are re-introduced as heated vapor into the aerosol forflow to the patient. Precipitate from the aerosol mixing chamber 144 isinitially collected on an area of the heater platen within the flow tubeand, under the differential pressure across the gap, flows into theaccumulator passage along the heater plate, providing longer and closercontact between the precipitate and the heater platen and, thereby, amore efficient heat transfer. Larger water droplets in the aerosol thatflows around the aerosol accumulator passage may be precipitated fromthe aerosol while the latter is in the accumulator passage. These arealso accumulated within the passage 172, to be collected on the heaterplaten 186 which forms the bottom of the passage. This water is alsore-vaporized by the heater platen for re-entrainment in the aerosolproduced by the system.

It is found that the described heating arrangement is exceedinglyefficient and provides surprising and greatly unexpected temperatureincrease for a given amount of heater power. In an arrangement of themixer body 120, heater 126 and container 122, connected without theaccumulator chamber 124 (the latter may be omitted from the assembly byproviding an adapter plate having a fitting at its upper end that mateswith the mixing chamber fitting and having its lower end mating with theheater housing threads), the heater was set to a temperature sufficientto provide a temperature of output aerosol in output tube 210 of between92° and 94° F., and required heater power was measured. The accumulatorunit 124 then was interposed between the mixer body and heater, asdescribed herein. Use of the accumulator provided the same outputtemperature of between 92° and 94° F. with only twenty percent of heaterpower required to obtain such temperature without the accumulator 124.

Illustrated in FIGS. 10 and 11 is a modified version of the heatednebulizer of FIGS. 6 through 9 which has changes made primarily toimprove collection and vaporization of precipitated water droplets andto provide a wider range of adjustment of vapor content and temperatureof the aerosol fed to the patient. The embodiment of FIGS. 10 and 11 isidentical to that of FIGS. 6 through 9 except for addition of a venturitube and modifications in heater and accumulator configuration.Identical parts in the two embodiments are designated by like referencenumbers.

The nebulizer head 320 of FIG. 10 is identical to the head 120 of FIG.5, except for the addition of a venturi tube 330. Tube 330 bothincreases flow velocity of aerosol into the mixing chamber 144, and,importantly, provides improved precipitated droplet collection. Venturitube 330 is fixedly positioned within the neck 332 of the mixer bodybelow the nozzle fitting 136 and has a lowermost portion of its shank334 cut away to form a large opening, as at 336. One side 337 of theshank extends downwardly to the end of the venturi tube 330 and hasfixed thereto a downwardly inclined bottom plate 338. The bottom plateinclines downwardly toward the wall 340 of the mixing chamber that iscloser to the axis of the mixing head and venturi tube, in thisasymmetrical arrangement of the mixing head that is shown in thedrawings. The lowermost free edge 342 of plate 338, which is offsetlaterally from the axis of the mixing head and the axis of the venturitube, has a downwardly projecting wedge shaped and pointed drip member344 fixed thereto. The plate also has an aperture 346 that snuglyreceives suction tube 140.

Venturi tube 330 acts to increase the velocity of the gas jet projectedfrom nozzle fitting 136 and also, by means of its bottom plate 338,collects water droplets. These collected droplets flow to the free edgeof the plate and then along the drip wedge 344 to drop from the point atits lower end. The pointed end of drip wedge 344 is positioned above theinwardly projecting floor 348 of the mixing chamber, and thus dropletsfrom the wedge 344 and also droplets flowing downwardly along theinterior walls of the mixing chamber tend to collect on the bottom wall348 of the mixing chamber to flow downwardly through the aperture 350thereof.

Droplets in the aerosol tend to collect on various surfaces, includingthe suction tube above the bottom plate 338. The snug fit of the bottomplate hole 346 around the exterior of suction tube 140 blocks the flowof collected droplets on the exterior of the suction tube and divertsthese droplets along the bottom plate to the drip wedge and then intothe accumulator passage, as will be described below.

Accumulator housing 351 includes a circular outer wall 354 and acircular inner wall 352 concentric therewith and integrally connectedwith the outer wall by an upper wall 356. The latter has an innerstepped vertical portion 358 that is spaced radially outwardly of anupper end portion 360 of the tubular inner wall 352. Tubular wall352,360 defines an inner or precipitate chamber 362 and cooperates withouter wall 354 to define the outer annular accumulator flow passage 364.The upper portion 360 of the tubular wall of the precipitate flowchamber 362 is radially spaced inwardly from the accumulator passagewall 358 and is externally threaded to receive the internally threadedconnecting nipple 148 of the mixing chamber 144. The accumulator chamberhousing has a lower end portion 366 that is externally threaded toreceive internal threads on an upper portion 368 of heater housing 370.An o-ring 372 has a relatively large diameter and is sufficientlyresilient and deformable to enable adjustment of temperature andmoisture content, as will be described below.

Heater housing 370 includes a heater chamber in which is mounted anannular heating element 371 positioned below a heated platen 374 thatforms the top of the heater housing and, concomitantly, the bottom ofthe accumulator chamber 364 and the bottom of precipitate or dropletflow chamber 362. The heater element extends only under the annularaccumulator chamber and not under the precipitate flow chamber 364. Atubular drain opening 378 extends through the heater housing and has anupper end substantially flush with the upper side of platen 374. Opening378, extending vertically through the heater and its platen 374, has arelatively large unrestricted diameter for free reception of the suctiontube 140. Accordingly, it is relatively easy, when assembling the mixerto the accumulator and heater units, to insert the free end of the long,slender and flexible suction tube 140 (having its upper end alreadyattached to the nozzle fitting 136) through the accumulator and heaterunits without any hands touching the suction tube. The large size ofthese openings, in both accumulator housing and heater, allows theoperator to hold only the mixer body and manipulate the free end of thelong, flexible suction tube through the openings of the heater andaccumulator units with little difficulty.

The lower end of the heater housing includes an internally threadedfitting 380 for threaded engagement with the externally threaded neck196 of a liquid container, and, if desired, may also have a largerthreaded opening (not shown), just as is illustrated with the heaterassembly of FIG. 6, for reception of a container having a largerdiameter threaded neck.

Integrally formed with the heater housing is a peripheral skirt 384 thatis radially outwardly spaced from the walls of housing 370 to act as aheat shield so that the heater assembly provides a relatively lowertemperature exterior surface.

Heated platen 374 is slightly dish-shaped, that is, concave upwardly,having a slope in the order of 2° to 3° from its outer peripheral edgedownwardly toward the center of the plate at the upper end of tubularopening 378. Just as in the embodiment of FIG. 6, a flexible connectingtube 176 is connected at one end to the mixing head discharge port 146and at the other to the input port 373 of the accumulator housing, whichalso has an output port 375 adapted to be connected via a conduit 210 toa patient.

An important feature of the described arrangement is adjustability ofthe water flow gap between the bottom end 390 of tube 352 and the heatedplaten 374. As previously mentioned, the o-ring 372 is relatively large,resilient and deformable. Further, the threads on parts 366,368, whichinterconnect the accumulator housing and heater housing, have a steeppitch. Accordingly, a small degree of rotation of the accumulatorhousing relative to the heater housing will axially shift theaccumulator relative to the heater but will still maintain sufficientcompression of the o-ring 372 so that the two are still sealed together.This small amount of axial relative shifting will change the size of thegap at the bottom end 390 of the precipitate flow chamber, and thus willadjust the amount of water that flows from the precipitate flow chamber362 to the accumulator chamber 364. By adjusting the gap between theprecipitate flow chamber and the accumulator chamber one can adjust theamount of heated water vapor that is added to the aerosol in theaccumulator chamber. Thus temperature and moisture content of theaerosol discharged to the patent are both adjusted, merely by relativerotation of the accumulator housing and heater housing.

If desired, the adjustment is arranged so that the gap can be adjusteddown to a very small size, such that effectively no water will flow fromthe precipitate flow chamber 362 into the accumulator chamber.Preferably, a rotation stop (not shown) is provided such that there is alimit on the minimum size of the gap which, therefore, is nevercompletely closed and will always allow some water to pass. Normally,however, the gap is adjusted to about 0.030 inches so that there will bean adequate flow of water for vaporization and combining with theaerosol in the accumulator chamber. For adjustment of the gap, it may bedesirable to provide indicia on the accumulator housing and heaterhousing to indicate a desired amount of relative rotation, and,therefore, the gap size.

The heated nebulizer of FIGS. 10 and 11 operates substantially in thesame way as the heater nebulizer of FIGS. 6 through 9. Pressurizedoxygen is introduced through the nozzle fitting to the interior of themixer body to suck water from the liquid container 122 via suction tube140. The suction tube extends from the container through the heater,through the droplet flow passage 362, which is circumscribed by theaccumulator flow passage 364, and through the aerosol mixing chamber.Ambient air is also pulled into the mixing head through the ports 137 sothat the aerosol stream is projected downwardly through and axiallyalong the center of venturi tube 330. The stream impinges upon thebottom plate 338 and is directed radially outwardly toward the walls ofthe mixing chamber 144, which may be provided with shallow ribs 340extending substantially vertically along the walls from top to bottomand spaced circumferentially about the mixing chamber. As the aerosol isdirected somewhat radially outwardly from the bottom plate 338, it tendsto travel in a circular path about the aerosol mixing chamber, impingingupon the ribs 340, which thus aid in precipitation of large droplets ofaerosol. These droplets are collected along the walls of the aerosolmixing chamber and flow down through opening 350 to accumulate at thelower end of precipitate flow chamber 362.

It is important to note that the lower end 390 of the tubular wall 352,which defines the precipitate flow chamber 362, is spaced slightly abovethe upper surface of the dish- shaped heated platen 374 to provide aliquid flow gap for flowing liquid from the bottom of the flow chamber362 into the accumulator chamber 364 along the platen 374. This flow isassisted by the pressurization of the interior of chamber 362, caused inpart by the pressurized oxygen coming into the mixing head. Pressurewithin chamber 362 is of course communicated to the interior of theclosed and sealed liquid container 122, but the accumulator chamber 364has its output port effectively connected to the patient, and thereforeto ambient pressure, which is lower than the pressure within theprecipitate flow chamber 362. Accordingly, the pressure differenceacross the gap at the bottom 390 of the precipitate flow chamber ensuresflow of the collected liquid into the accumulator chamber. Droplets arealso collected by the venturi tube bottom plate 338, which blocks flowof liquid that adheres and to and tends to flow downwardly along theexterior surface of the suction tube 140. Plate 338 and its drip wedge344 tend to direct such collected droplets to the bottom 348 of theaerosol mixing chamber, from whence it flows downwardly through theprecipitate tube 352, to be collected at the bottom of chamber 362. Thedrip wedge 344 helps to prevent water running downwardly along the uppersurface of the plate 338 over the lower edge and then back up along thebottom side of the bottom plate toward the pickup tube 140. As theliquid flows through gap 390 along the heated platen to the bottom ofthe accumulator flow chamber 364 it is heated and at least some isvaporized by the high temperature of this outer annular section of theheated platen. Thus heated water vapor is generated to mix with theaerosol within the chamber 364, thus increasing both its water contentand temperature. By adding heated water vapor, temperature of theaerosol mixture is most efficiently increased.

The described arrangement of FIGS. 10 and 11 includes a safety featurethat prevents significant overheating, such as may cause danger to theoperator and deformation or destruction of the mixer head. If the oxygensupply is turned off without turning the heater off, water contained inthe bottom of the accumulator chamber 364 will flow radially inwardlyalong the tapered platen to the drain tube 37 and drain back into thecontainer itself. If provision were not made for draining of water fromthe accumulator chamber upon shut off of the oxygen, water containedwithin the accumulator chamber 364 would start to boil upon shut off ofthe oxygen, since there would be no longer any flow through theaccumulator passage. Steam then would tend to fill the accumulatorpassage and flow back up through the connecting tube 176 into the mixerhead itself. The latter is made of a plastic that may tend to deform attemperatures in the order of 100° C. or less, and thus can be seriouslydamaged by being filled with steam. Moreover, the heater and other partsof the instrument may become excessively hot to the touch if steamcontinues to be generated after oxygen is turned off. However, this isnot possible with the described arrangement, because the water willdrain back to the container and will not be boiled or turned into steam.Moreover, the heat shield 384 helps to maintain a lowered externaltemperature of portions of the instrument adjacent the heater.

An advantage of the recessing of threaded portion 360 of the accumulatorhousing within the accumulator housing itself is the fact that thisdecreases the overall height of the instrument, and, in particular,decreases the distance between the liquid container 122 and the mixinghead. The nebulizer nozzle fitting pulls liquid from the container bymeans of suction produced by the high velocity jet, and is able to suckliquid over only a limited vertical distance. The less the length(vertical extent) of the accumulator and heater units, which areinterposed between the mixing head and the container, the less thedistance through which the liquid need be drawn up from the container.

The described apparatus is considerably quieter than prior nebulizers,providing less jet venturi noise from the mixing head and considerablyless noise in the tube that connects the accumulator output to thepatient. The decrease in noise in due in part to the multiple chambersand the flow paths for the aerosol.

Prior nebulizers are limited in the amount of flow rate available,because if flow rate is increased, the temperature of the generatedaerosol is decreased. With the present apparatus, however, flow to thepatient can be increased to as great as 110 liters per minute and stillmaintain a temperature of greater than 90° F. at the patient. With allprior nebulizers at such a flow rate temperatures as high as 85° F. aredifficult, if not impossible, to obtain. In prior nebulizers, as flowrate increases above 50 liters per minute, temperature decreases at arelatively fast rate. With the arrangement described herein, on theother hand, if flow rate is increased (by increasing the flow rate ofoxygen provided to the mixer head), an increased amount of water isdriven to the heated platen at the bottom of accumulator chamber 364because of the increased pressure difference between chambers 362 and364. Therefore, more water on the platen is vaporized and a greateramount of heat is added to the aerosol. Accordingly, with the describedarrangement, as flow rate increases temperature may decrease, but willdecrease at a significantly lower rate than it does with prior devices.

With the apparatus described in FIGS. 10 and 11, it is possible toprovide an aerosol having 40 milligrams of water per liter of aerosol atthe patient at a temperature of 94° F. In prior nebulizers, a maximum of30 milligrams of water per liter was available at significantly lowertemperatures.

A significant factor in the nebulizers described herein, particularlythe embodiments of FIGS. 6 through 9 and FIGS. 10 and 11, is the factthat the instruments are configured and arranged for collectingparticulate dropout and vaporizing the collected particulate so as tointroduce heated water vapor into the aerosol, instead of sending theparticulate dropout back into the container, as is the case with priordevices. In most prior devices little or no precipitated water dropletsare heated, and almost none are vaporized for mixing with the aerosol.In the described arrangement, collection of particulate fallout ismaximized, and all of the fallout may be fed to the heated bottom of theaccumulator chamber for vaporization and re-introduction into theaerosol.

Operation of the nebulizers described herein, and in particular thenebulizer illustrated in FIGS. 10 and 11, is carried out at total outputflow rates (from output tube 210) in the range of about 15 to 80 litersper minute of moisturized gas. This output flow rate is controlled bythe rate of flow of oxygen into the mixing body from the oxygen inputtube, such as tube 134 of FIG. 6. With the input of oxygen controlled toprovide a total output in the range of between about 15 and 80 litersper minute, the nebulizers described above operate in a fullysatisfactory manner as described herein. However, in some applicationsthe nebulizers may be operated to provide a total output flow outside ofthis range. Thus, for example, the input oxygen flow rate may be turneddown sufficiently to cause a total output flow rate of less than 15liters per minute. These nebulizers are sometimes used to provide totaloutput flow rates as low as 8 liters per minute. In such a situation, atleast in part because of the very low input oxygen flow, there issubstantially no pressure differential across the gap between the lowerend of the precipitate flow tube 170 or precipitate chamber inner wall352 and the accumulator flow passage 172 (FIG. 6) and 364 (FIG. 10).Without this differential pressure droplets collected at the bottom ofthe precipitate chamber 362, for example, do not flow into the flowpassage 364, and therefore the increase in water vapor which is achievedat higher total output flow rates by vaporization within the chamber364, does not occur. At such lower total output flow rates there may beno water flowing along the heater platen 374 from the precipitatechamber, and therefore the output mixture may not be sufficientlymoisturized by added water vapor in the accumulator chamber.

A somewhat analogous situation (e.g. lack of water vapor added in theaccumulator chamber) occurs at very high total output flow rates, thoseabove about 80 liters per minute. If the oxygen input rate is very high,or if a secondary gas (such as air) input is provided to the mixer body,as by an auxiliary pressurized air input of the nebulizer shown in U.S.Pat. No. 4,767,576 for Nebulizer With Auxiliary Gas Input, the pressurewithin the precipitate chamber 362 may be so high that an excess amountof water is driven by this pressure through the gap at the lower end ofthe inner wall 352. Under such conditions the flow passage 364 (FIG. 10)becomes filled or nearly filled with a body of turbulent water in aquantity too great for the heater to vaporize.

In operation within the normal total output flow range, between about 15and 80 liters per minute, the pressure differential is such that waterflows from the precipitate chamber 362 through the gap and into the flowpassage 364 at a rate approximately equal to the rate at which theheater vaporizes water at the bottom of the accumulator chamber. In sucha situation the differential pressure provides a relatively thin film orrelatively small depth of water on the heater platen 374 within flowpassage 364. Therefore only a small volume of water is presented to theheater platen at any given time for vaporization. For the vaporizationof water by the heater to be most efficient and effective, the waterflowing into the flow passage, which is effectively the vaporizationchamber of the heater, must be at a rate sufficient to replace thatwhich is vaporized by the heater. Moreover, water must not accumulate insuch a volume within the flow passage 364 as to exceed the ability ofthe heater platen to vaporize the water. In other words, there may beinadequate vaporization by the heater when (a) there is no water on theheater platen with the accumulator chamber, or (b) there is too muchwater for the heater capacity.

Although adjustability of the gap between the lower end of innercircular wall 352 and the heated platen is available by means of thethreaded interengagement of the heater housing and accumulator housing,such a fine adjustment by the user is not always possible in the fieldbecause the technician may have insufficient time or insufficientexperience and training to establish the appropriate adjustment.Therefore it is desirable to provide for automatically controlled properflow rate from the precipitate chamber to the accumulator chamber at alltotal output flow rates, including those below and above the range of 15to 80 liters per minute.

Illustrated in FIGS. 12 and 13 is a slightly modified embodiment of thenebulizer of FIG. 10 in which the problems caused by total output flowrate that is either too low or too high are substantially avoided or atleast significantly alleviated. This improvement is accomplished byinducing flow from the precipitate chamber 362 to the flow passage 364and controlling the rate of such flow, to as to maintain at all times asuitable low depth of water on the heater platen within the accumulatorchamber. To this end a flow inducing flow rate control member ispositioned in the gap between the heater platen and the lower end of thecircular inner wall 352 or the lower end of wall 170 of FIG. 8.

Conveniently, the flow inducing and flow rate control member is made ofa mass transfer medium in the form of a capillary matrix. The capillarymatrix is formed as a thin centrally apertured disc of a wickingmaterial such as blotting paper, open cell foam or a porous solid. In aparticular example a conventional chromatographic paper has been used.Preferably the wicking disc (of chromatographic paper) has a thicknessof between about 5 and 30 mils in dry state (it may expand when wet).Water that is placed in contact with one portion of the disc is inducedto flow to other portions of the material by wicking or capillaryaction. Such an annular disc is illustrated as a wicking disc 400 inFIG. 12, having an inner aperture 402 that is smaller in diameter thanthe diameter of inner circular wall 352 of the precipitate chamber ofFIG. 10 and having an outer diameter that is substantially equal to thediameter of the outer wall 354 of the accumulator housing. The wickingdisc 400 is merely inserted between the accumulator housing and theheater platen in the manner illustrated in FIG. 13. It just rests uponthe platen. No parts of the heater or other parts of the assembly shownin FIG. 10 need be changed for use of the wicking disc 40. FIG. 13 showsparts of the nebulizer heater which are identical to and arranged in amanner identical to the corresponding parts of the embodiment of FIG. 10The only difference between the devices of FIGS. 13 and 10 is theinsertion in the device of FIG. 13 of the wicking disc 400. The disc isplaced on the upper concave side of platen 374 and effectively held inplace and clamped between the platen and the lower edges of the circularinner wall 352 and also clamped at the outer edges of the disc betweenthe lower edges of the circular outer wall 354 and the outer edge of theplaten 374.

The arrangement of the disc clamped between the accumulator housing andprecipitate chamber on its upper side and the heater platen 374 on itslower side is illustrated in enlarged detail in FIG. 13. Thus, as can beseen in FIG. 13, lower edge 390 of the inner circular wall 352 clampsagainst an upper side of the wicking disc 400 radially outwardly of itsinner edge 402. Similarly, a lower edge 410 of the outer circular wall354 of the accumulator housing is pressed down against the upper side ofthe outer periphery of wicking disc 400, clamping this outer edgebetween the outer edge of the platen and the accumulator housing. Aninner portion 112 of the disc lies in the precipitate chamber to receiveprecipitated droplets. Effectively, the wicking disc acts as a kind of aporous flow inducing barrier which prevents high flow rates of waterthrough the gap (analogous to gap 202 of FIG. 8) between the wall end408 and the heater platen.

With the arrangement of the wicking disc 400, as shown in FIGS. 12 and13, a flow of water from the precipitate chamber 362 to the flow passage364 along the platen and through the gap at the lower end of wall 352 isautomatically maintained at an even controlled rate throughout a muchwider range of total output flow rates. The flow induced by wickingaction automatically adjusts its rate to replenish the water given up inthe accumulator chamber to the aerosol by vaporization. The wicking discoperates to remain wet at all times, thus maintaining a volume of wateron the heated platen that is within the power of the heater to vaporize.If the total rate of the nebulizer is less than 15 liters per minute,down to as low as 8 liters per minute or less, for example, so thatthere is little or no differential pressure to drive the water over theheater platen through the gap, the wicking action of the disc 400 issufficient to induce flow of water from the precipitate chamber 362,through and along the wicking disc into the lower end of flow passage364. The water that is caused to flow by the wicking action of the disc400 effectively saturates the disc but does not flow at a ratesufficient to cause any significant amount of standing water on theupper surface of the disc within the flow passage 364. Effectively, thedisc operates to remain saturated with water as long as there is waterbeing provided to the inner portion of the disc, namely that portionindicated at 412 in FIG. 14, that is inward of the wall 352. As theheater heats the water contained in the outer portions of the wickingdisc 400, within the flow passage 364, such water is vaporized and takenup by the aerosol mixture flowing through passage 364. As this water isvaporized the wicking action induces flow of additional water from theprecipitate chamber, and thus a continuous flow of water from theprecipitate chamber is induced by the wicking disc to automaticallyreplenish water that is vaporized by the heat supplied by the heater.The wicking disc is effectively self-adjusting with regard to flow rateof water from the precipitate chamber to the flow passage and willoperate at total aerosol output flow rates considerably below the normal15 to 80 liters per minute flow rate.

Should the nebulizer be operated at very high total output flow rates,in the order of more than 80 liters per minute, so that a greaterdifferential pressure is created, with a higher pressure within theprecipitate chamber 362, the wicking disc acts as a flow controllingbarrier that allows a limited amount of water to flow from the innerprecipitate chamber to the outer flow passage. Thus, the presence of thewicking disc not only ensures some flow at very low total output flowrates, but prevents too great a flow at very high total output flowrates. Accordingly, over a greatly increased range of total output flowrates, the heater platen is provided with an optimum amount of water formost efficient vaporizing action.

As previously mentioned, the controlled flow rate induced by the wickingdisc 400 cooperates with the heater and heated platen to maintain arelatively small volume of water covering the platen so that the heatedplaten vaporizes the water at approximately the same rate as the wateris induced to flow through the wicking disc from the central precipitatechamber. The wicking member enhances the efficiency of the vaporizationin several ways. First, it controls the depth of water above the platenand the rate of replenishment of water that is vaporized. In additionthe wicking member provides a much greater surface area of water and ofthe capillary matrix itself to which heat from the platen may betransferred. Thus, a greatly increased surface area is provided toreceive heat from the platen, and, effectively, a greater amount ofwater is thereby vaporized.

There have been described improved nebulizer heater assemblies whichemploy but a single heating unit to heat both the liquid in thenebulizer container and the aerosol produced by the nebulizer, while atthe same time collecting rain out from the produced aerosol andreintroducing the collected rain out as water vapor into the aerosol.

The foregoing detailed description is to be clearly understood as givenby way of illustration and example only, the spirit and scope of thisinvention being limited solely by the appended claims.

What is claimed is:
 1. For use with a nebulizer having a mixing headincluding a mixing chamber for producing aerosol, said chamber having alower connecting section with a lower opening therein, said chamber alsohaving an outlet port for discharging aerosol, an improved heaterassembly comprising:a heater chamber, a heater in said chamber, a heatedplaten extending across said heater chamber at an upper end thereof, anaccumulator housing having:an axially extending central chamber with alower end adjacent said heated platen, said central chamber beingconfigured and arranged to collect droplets of liquid precipitated fromsaid aerosol, an outer annular chamber circumscribing said centralchamber, said annular chamber having input and output ports, means on anupper portion of said accumulator housing for connecting said housing tosaid mixing head with said central chamber in communication with saidlower opening of said lower connecting section of said mixing chamber,and means for flowing liquid collected in said central chamber to saidouter annular chamber to be heated and vaporized by said heated platen,means on a lower portion of said accumulator housing for connecting saidhousing to said heater chamber with said platen forming a bottom of saidouter annular chamber, and means for flowing aerosol from said outletport into said annular chamber input port.
 2. The heater assembly ofclaim 1 wherein said heated platen forms a bottom of said annularchamber, and wherein said central chamber lower end cooperates with saidplaten to define a gap, said gap forming said means for flowing liquidcollected in said central chamber to said outer annular chamber.
 3. Theassembly of claim 2 including means for adjusting said gap to adjustrate of flow of liquid from said central chamber to said annularchamber.
 4. The assembly of claim 1 wherein said heated platen isconcave upwardly, and includes a drain port in a lowermost portionthereof.
 5. The assembly of claim 1 wherein said central chamber isconfigured and arranged to be pressurized via said lower opening by anebulizer mixing head connected to said accumulator housing, said heatedplaten having a low portion at said central chamber lower end, andhaving a drain in said low portion, whereby liquid droplets that fallout of said aerosol will flow through said lower opening of said mixingchamber into said central chamber, and whereby droplets collected insaid central chamber will flow from the lower end of the central chamberinto the annular chamber when the central chamber is pressurized, andwill flow out through said drain port when said central chamber is notpressurized.
 6. The heater assembly of claim 1 wherein said means forflowing liquid collected in said central chamber comprises means forinducing a controlled flow rate of liquid from said central chamber tosaid outer chamber.
 7. The heater assembly of claim 6 wherein said meansfor inducing a controlled flow rate comprises a capillary matrix.
 8. Theheater assembly of claim 6 wherein said means for inducing a controlledflow rate comprises an annular disc of chromatography paper.
 9. Theheater assembly of claim 6 wherein said means for inducing a controlledflow rate comprises an annular disc of blotter paper.
 10. The heaterassembly of claim 6 wherein said means for inducing a controlled flowrate comprises an annular disc of a capillary matrix.
 11. The heaterassembly of claim 6 wherein said means for inducing a controlled flowrate comprises a wicking disc interposed between the lower end of saidcentral chamber and said platen.
 12. The heater assembly of claim 1wherein said central chamber lower end cooperates with said platen todefine a gap, and including a body of a mass transfer materialpositioned in said gap and extending on both sides of said gap.
 13. Aheater assembly comprising:a heater chamber, a heater in said chamber, aheated platen extending across said heater chamber at an upper endthereof, an accumulator housing having a wall dividing the housing intoa precipitate chamber and a flow passage, said precipitate chamberincluding means for receiving liquid,said accumulator flow passageincluding means for receiving a gas mixture and means for dischargingsaid mixture therefrom, and means for inducing flow of liquid from saidprecipitate chamber to said flow passage.
 14. The heater assembly ofclaim 13 wherein said means for inducing flow comprises a capillarymatrix.
 15. The heater assembly of claim 13 wherein said means forinducing flow comprises a body of wicking material extending from saidprecipitate chamber to said flow passage.
 16. The heater assembly ofclaim 13 wherein said means for inducing flow includes means forlimiting flow from said precipitate chamber to said flow passage. 17.The heater assembly of claim 13 wherein said means for inducing flowincludes means for covering said platen with a relatively small volumeof liquid, whereby said heated platen may vaporize liquid covering theplaten at a rate substantially equal to the rate of flow of liquid fromsaid precipitate chamber to said flow passage.
 18. The heater assemblyof claim 13 wherein said mean for inducing flow comprises meanscooperating with said heater to maintain a relatively small volume ofliquid covering said heater platen.
 19. For use with a nebulizer havinga mixing head including a mixing chamber for producing aerosol, saidchamber having a lower connecting section with a lower opening therein,said chamber also having an outlet port for discharging aerosol, animproved heater assembly comprising:a heater chamber, a heater in saidchamber, a heated platen extending across said heater chamber at anupper end thereof, an accumulator housing having:a central precipitatechamber configured and arranged to collect droplets of liquidprecipitated from said aerosol, an outer chamber circumscribing thecentral chamber and having input and output ports, means on an upperportion of the accumulator housing for connecting the housing to amixing head, with said central chamber in communication with the loweropening of the lower connecting section of the mixing chamber, and meansfor inducing flow of liquid at a controlled flow rate from said centralchamber to said outer chamber to be heated and vaporized by said heatedplaten, and means on a lower portion of said accumulator housing forconnecting said housing to said heater chamber with said platen forminga bottom of said outer chamber.
 20. The heater assembly of claim 19wherein said means for inducing flow comprises a flow passage betweensaid central chamber and outer annular chamber and mass transfer meansin said flow passage.
 21. The heater assembly of claim 20 wherein saidmass transfer means includes a body of wicking material extending from apoint within said central chamber to a point in said outer annularchamber.
 22. The heater assembly of claim 21 wherein said body ofwicking material lies along an upper surface of said heated platen. 23.The heater assembly of claim 19 wherein said heated platen has an uppersurface forming a bottom of said outer chamber, and wherein said meansfor inducing flow comprises an annular wicking disc extending from saidcentral chamber to said annular chamber and having a portion thereoflying on said upper surface of said heated platen within said annularchamber.
 24. The heater assembly of claim 19 wherein said heated platenhas an upper surface forming a bottom of said annular chamber, whereinsaid central precipitate chamber has a lower end positioned adjacent tobut spaced from said heated platen surface, and wherein said means forinducing flow comprises a flow inducing member extending along saidheated platen surface between said lower end of aid central precipitatechamber and said heated platen surface.
 25. The heater assembly of claim19 wherein said heated platen has an upper surface forming a bottom ofsaid outer annular chamber and wherein said central precipitate chamberhas a lower end positioned adjacent to and spaced from said heatedplaten upper surface, said means for inducing flow comprising a thindisc of a capillary matrix positioned in contact with said heated platensurface and extending between said surface and said lower end of saidcentral chamber from a position within said central chamber to outerportions of said heated platen.
 26. A heater assembly comprising:anaccumulator housing defining an accumulator chamber having input andoutput ports,said accumulator chamber including means for receiving anaerosol mixture of gas and liquid vapor at said input port anddischarging said mixture from said output port. a precipitate collectionchamber having a precipitate input port adapted to receive liquidprecipitate, heating means for vaporizing liquid in said accumulatorchamber, and means for inducing liquid flow at a controlled rate fromsaid precipitate collection chamber to said accumulator chamber.
 27. Theheater assembly of claim 26 wherein said means for inducing liquid flowcomprises a wicking member extending between said precipitate collectionchamber and said accumulator chamber.
 28. The heater assembly of claim26 wherein said heating means includes a heater platen, and wherein saidmeans for inducing liquid flow comprises a capillary matrix extendingfrom said precipitate collection chamber to said accumulator chamber andhaving a portion in contact with said heater platen.